利用Servlet和jsp实现客户端与服务器端的用户登录信息验证

首先编写登录页面mylogin.jsp

编写表单：

<form onsubmit="return valdate()">
  
  username:  <input type="text" name = "username" id="username"><br/>
  password:  <input type="password" name = "password" id="password"><br/>
  repassword:  <input type="password" name = "repassword" id="repassword"><br/>

  <input type="submit" value="submit"/>
  <input type="reset" value="reset"/>  
  
  
  </form>

第一种验证的方式：利用javascript在客户端实现验证

 <script type="text/javascript">
  
  function valdate(){
  //var username = document.getElementById("username");
  //var password = document.getElementById("password");
  //var repassword = document.getElementById("repassword");
  
   var username = document.getElementsByName("username")[0];
  var password = document.getElementsByName("password")[0];
  var repassword = document.getElementsByName("repassword")[0];
  
  if(username.value.length == 0){
   
   alert("username can not be blank");
   return false;
  }
  
  if(password.value.length < 6 || password.value.length > 11){
  
    alert("length of password is invalid");
   return false;
  
  }
  if(password.value != repassword.value> 11){
  
    alert("password is not the same with repassword");
   return false;
  
  }
   return true;
    
  }
  
  
  </script>

如上面的代码所示，在表单中调用javascript的函数实现客户端验证。

第二种验证的方式：用Servlet实现验证

编写ValidateServlet.java类

package com.lcq.servlet;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@SuppressWarnings("serial")
public class ValidateServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String username = request.getParameter("username");
		String password = request.getParameter("password");
        String repassword = request.getParameter("repassword");
        List<String> list = new ArrayList<String>();
		if(null == username || "".equals(username)){
			list.add("username can't be blank!");
		}
		if(password == null ||password.length() < 6 ||password.length() > 10){
			list.add("length of password should be between 6 and 10");
		}
		if(repassword == null ||repassword.length() < 6 || repassword.length() > 10){
			list.add("length of repassword should be between 6 and 10");
		}
		if(password != null && repassword != null && !password.equals(repassword)){
			list.add("password and repassword not the same!");
		}
        
		
		if(list.isEmpty()){
			request.setAttribute("username", username);
			request.setAttribute("password", password);
			request.getRequestDispatcher("sucess.jsp").forward(request, response);
		}else{
			request.setAttribute("error",list);
			request.getRequestDispatcher("error.jsp").forward(request, response);;
		}
       
        
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
         doGet(request, response);
	
	}

}

在Servlet中处理完成后转到sucess.jsp或者error.jsp

以下是sucess.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
  
    
    <title>My JSP 'sucess.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>
  
  
  username :<%=request.getAttribute("username") %><br>
  password :<%=request.getAttribute("password") %>
 
  </body>
</html>

以下是error.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    
    <title>My JSP 'error.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>

  <h1>login failed:</h1>
  <%
  List <String> list = (List<String>)request.getAttribute("error");
  for(String str : list ){
  out.println(str + "<br>");
 
  }
   %>
    





  </body>
</html>

用第二种方式时将mylogin.jsp中的表单修改为